Comprehensive two-dimensional gas chromatography (GC x GC) with flame ionization detection has been applied to oil spill source identification. An oil spill case from the U.S. Coast Guard's Marine Safety Laboratories (MSL) was analyzed by GC x GC. A slightly weathered, marine diesel fuel spill sample was qualitatively and quantitatively compared to two potential source samples. The high resolving power of GC x GC separated several hundred components from the petroleum matrix. Compounds of similar chemical structure were grouped together in an ordered two-dimensional chromatogram. In these ordered groups, numerous small peaks representing minor components were separated and detected. This was especially helpful in determining compounds and compound classes to be used in the analysis. Several classes of compounds were found to be useful for comparing the samples, including alkanes, cycloalkanes, alkylbenzenes, alkylnaphthalenes, and anthracene/phenanthrenes. The GC × GC analysis resulted in a match between the spill sample and one of the source samples. This result was consistent with HRGC and GC/MS analyses employed by the MSL.